In genetic and cytological studies of the haploid fungus Neurospora, chromosome rearrangements are being analyzed and used for a variety of problems. Several types (e.g., insertional translocations) recurrently generate via meiosis a class of viable progeny containing nontandem duplications. Their properties are of interest for comparison with similar rearrangements in diploid organisms, including man, where direct study is difficult. Duplication-generating aberrations are being used for studying vegetative incompatibility, regulation, complementation and dominance, and mapping by duplication coverage. Many duplications show instability due to deletion, and this is subject to genetic modification. These are being used in a search for control systems that regulate deletion. Mutants that affect meiosis are being studied. Cytological studies also concern chromosomal structure and behavior both in meiosis and mitosis, the cellular basis of barrenness and of the ascospore abortion that is characteristic of interspecific and of some intraspecific crosses, and the behavior of replicating acentric chromosome fragments. Strains of Neurospora from nature are being used as a source of genic and chromosomal variants. Three Spore-killer (SK) genes have been identified that show meiotic drive. In heterozygous crosses these result in death of meiotic products that contain the normal SK ion allele. BIBLIOGRAPHIC REFERENCES: Perkins, D. D. (1975). The use of duplication-generating rearrangements for studying heterokaryon incompatibility genes in Neurospora. Genetics 80: 87-105. Perkins, D. D., B. C. Turner and E. G. Barry (1975). Neurospora from nature. (Abstr.) Genetics 80: s63.